1. Field of the Invention
The present invention relates generally to optical disc drives and more particularly to an optical disc drive suitable for use with optical information processing apparatus such as a magneto-optical disc drive and so on.
2. Description of the Prior Art
FIG. 1 schematically illustrates an arrangement of, for example, a conventional optical disc drive.
Referring to FIG. 1, a conventional optical disc drive mainly comprises a pair of guide rods 3A and 3B, an optical pickup 4 and an objective lens bobbin 6 having an objective lens 7 and rotatable around a rotary shaft 5 provided on the optical pickup 4 at its center. The pair of guide rods 3A and 3B are extended along the radial direction of a magneto-optical disc 1. The optical pickup 4 moves along the pair of guide rods 3A and 3B in the direction shown by an arrow b such that it traverses recording tracks 2 formed on the magneto-optical disc 1 which rotates in the direction shown by an arrow a. The objective lens bobbin 6 rotates around the rotary shaft 5 by a very small amount in the direction shown by an arrow c.
The objective lens 7 is mounted on the objective lens bobbin 6 at the position deviated in the direction perpendicular to the guide rods 3A and 3B from the rotary shaft 5 such that it irradiates a light beam spot on the magneto-optical disc 1. Thus, when the optical pickup 4 moves along the guide rods 3A and 3B in the direction shown by an arrow b, the light beam spot irradiated on the magneto-optical disc 1 from the objective lens 7 moves to cross the recording tracks 2, thus to seek a recording track to be accessed. In other words, a so-called seek operation is performed.
When the light beam spot irradiated from the objective lens 7 reaches the recording track to be accessed, if the objective lens bobbin 6 is controlled (fine-tracking-controlled) to rotate in the direction shown by the arrow c on the basis of a tracking error signal, the objective lens 7 is urged to move in the widthwise direction of the recorded track 2 in the direction shown by the arrow d by a very small amount. Thus, such a tracking-controlling is effected that the light beam spot from the objective lens 7 follows the target recording track 2.